Tamping plug



United States Patent O 1 Claim. (Cl. 102-30) and Chester M. Pomeroy,

I. du Pont de Ne- Del., a corporation The present invention relates to a novel tamping plug especially suitable for use in smaller diameter boreholes.

The stemming of boreholes is widely used to protect loaded explosive charges in a borehole from accidental ignition from fire or sparks, to retain the charges in proper relationship within a borehole when rotational or delay firing is practiced, and to increase the confinement of the borehole to increase the efiectiveness of the explosive charges. For many years, loose stemming materials, such as sand, clay, ground limestone dust, or mud have been used, and are the preferred stemming for vertical boreholes, particularly above ground where such materials are readily available. For underground mining, particularly of coal, the use of loose stemming is less satisfactory both because the boreholes are generally not vertical and because the stemming must be provided from a remote source.

For many years, dummies," i.e., tamping bags containing loose stemming material, or clay plugs made of extruded plastic clay, have been used as tamping in horizontal or sloping boreholes, and in more recent years, a tamping plug of pleated asbestos has gained wide usage. The dummies and clay plugs provide satisfactory stemming only when a large quantity is used, because the stemming has little resistance, other than its own weight, toward being forced out of the hole. The pleated asbestos tamping plug, which is expanded inside the borehole by a wedge-like solid piece of wood or ceramic material, provides excellent confinement, but suffers from the disadvantage that the creation of a good seal is dependent upon the proper driving of the wedge. Also, a number of accidents have been caused by the discharge of the wedge from the borehole as a projectile when the charge is initiated.

An object of the present invention is to provide an improved blasting plug. A further object is to provide a plug simple to position and elfective in sealing the borehole and safe to use. Additional objects will become apparent as this invention is more fully described.

We have found that the foregoing objectives may be achieved when we provide as a blasting plug a unitary cylinder having a plurality of flexible radial fins, the diameter of the cylinder being approximately /2 the diameter of the fins. The plug having the above described construction will preferably be a one-piece fabrication and we prefer to use a synthetic polymer, particularly polyethylene or polyvinyl chloride, as the fabrication material.

In order to more fully describe the present invention, reference is now made to the accompanying drawings, in which Figure 1 illustrates the tamping plug of the present invention and Figure 2 represents a loaded borehole in which the tamping plug of this invention has been introduced.

Referring now to the figures, 1 represents a cylinder, 2 represents flexible radial fins, 4 represents explosive cartridges,

3 represents a borehole, and 5 represents lead-in "ice A wires to any initiating device located in therear of the borehole (not shown).

- The tamping plug of this invention can be prepared by conventional means, such as by compression or in- -jection molding, and will be fabricated from a material which will retain flexibility throughout the temperature range normally encountered in various types of blasting operations, i.e., from about l0 F. to F. Polyethylene and polyvinyl chloride compositions have been found very satisfactory.

In use, the tamping plug of this invention is inserted into the borehole after the explosive charges and initiating means have been introduced in the conventional procedure, and will be pressed into contact with the last charge. The tamping plug selected should have an overall diameter of from 10 to 20% in excess of the average diameter of the borehole, so that when the plug is forced into the borehole, the radial fins will be deformed into the shape of rearwardly directed cups.

When the charge is initiated, the tamping plug of the present invention will provide the temporary confinement required to increase the effectiveness of the explosive and will then be completely disintegrated by the blast. The absence of any metal or non-combustible dense solid parts eliminates the danger of projectile discharge from the borehole. Prior to the initiation of the charge, the retaining action of the deformed fins is sufiicient to prevent any dislodging of the charges from the vibration caused by nearby blasts, and effectively seals the borehole from the entrance of sparks or fire which could cause accidental ignition.

'The effectiveness of the retaining action of the tamping plug of the present invention is shown by the following example.

A polyethylene tamping plug prepared as illustrated in Figure 1 had a cylindrical body having an outside diameter of 1 inch and a wall thickness of inch. Integral with the body were 9 radial fins having a thickness of & inch and an overall diameter (including the cylindrical core) of 1% inches. This plug was inserted into the'end of a steel pipe having an inside diameter of 1 /2 inches far enough so that the entire plug was within the pipe. The leading fins may be smaller in diameter to allow insertion without difliculty.

Air pressure was then applied to the other end of the pipe. The plug made an airtight seal and held until the pressure within the pipe reached pounds per square inch, at which time the plug was forced out of the pipe.

In the preferred embodiment of our invention, the cylindrical body will be hollow in order to reduce the quantity of material required in the fabricationof the plug. However, the use of a solid body is entirely within the scope of this invention. 'It may be desirable to load flame quenching salts, such as sodium chloride or sodium carbonate inside the body of the blasting plug if the plug is to be used for permissible blasting. The plug of this invention can be inserted in either direction so that lack of care on the part of an operator will not affect the holding power. Many other modifications will be apparent to those skilled in the art, and we intend, there- References Cited in the file of this patent UNITED STATES PATENTS Halverson Aug. 12, 1930 Noble Sept. 6, 1938 Madill Mar. 24, 1953 FOREIGN PATENTS Belgium Jan. 15, 1952 France v May 13, 1953 

